LIGO MIT News

- Contributed by Rana Adhikari

Earlier this year, a "suggestion" was made to a certain freshman
graduate student at MIT (namely, me) that he spend some time at the
LIGO Hanford Observatory. His mission was apparently to "shakedown"
and "characterize" the 2K interferometer's 15-meter Mode Cleaner.

So plans were made and tickets were bought. And as the time to
depart for the site drew nigh, he periodically asked himself
questions, such as:

-- What exactly does "shakedown" mean? And won't that hurt the
equipment?

-- For that matter, what does characterize mean? And how can a
set of three mirrors have character?

-- How am I supposed to characterize something which hasn't been
installed?

-- What's a Mode Cleaner? (which was since answered eloquently
by Fred Raab in the
June 1999 issue).

So, with these vital questions largely unanswered,
this grad student headed out to the Washington desert...

First Sight

After two years as an undergraduate at the University of Florida,
bothering the Input Optics group, I still hadn't seen a single
piece of LIGO. But I had spent countless hours calculating,
simulating, and prototyping pieces of the subsystem. So it was
with awe when I saw for the first time this humongous thing that
I had previously known only through drawings.

At the outset of my stay, I spent a few weeks at work on hooking
up and testing a piece of the monstrous data acquisition system,
namely the fast channels (>2kHz) of the pre-stabilized laser.
The thinking here was that this knowledge would parlay easily into
doing the same for the Mode Cleaner (MC). I give many thanks to
Rick Savage and Dave Barker for helping me to understand the
electronics and software. The size of the 4-pin LEMO connectors
were measured to within about 1/4" for cable fitting using the
"Ocular Vernier" technique I developed while in kindergarten.

Seeing as the MC still had no character, I decided to get in on
its installation and alignment (see Figure 1 above). So for the next few weeks we
(Dan Dickerell, Peter Fritschel, Bill Kells, Nergis Mavalvala,
Guido Mueller, Haisheng Rong, Dave Tanner and I) climbed around
Horizontal Access Modules (HAM) 7 and 8 like ants in their tunnels.
The long, long hours put in by these people resulted in the
success captured by the
pictures
of the laser beam shown in last month's newsletter.

Photo Fest

Above: (Left) From left to right, Dave Tanner, Dan Dickerell,
and Guido Mueller from in front of the west side of HAM7.
(Right) Starving grad student demands of Peter Fritschel that
he be allowed to get some lunch or he will,"...huff and puff
and blow your interferometer down!"

Below: (Left) Shot of the Mode Cleaner's two flat mirrors
(MC1 & MC3) in their respective Small Optics Suspensions.
The large optic in the Large Optic Suspension on the right is
the last Mode Matching Telescope mirror. (Right) Inside HAM8
the Mode Cleaner's curved mirror (MC2) standing proudly in front
of the incredibly baffled Recycling Mirror.

One of the most inspiring things I witnessed this summer was
the coordinated way in which things progressed (at least, most
of the time). It seemed that as soon as we would hit a snag,
whoever it was in the LIGO community that had the solution
would just "happen" to show up, almost as if it had been
planned ahead of time.

Living With the Mode Cleaner

Having the opportunity to spend over two months living with
the Mode Cleaner (see Figure 6 at right) allowed me to get to work with anyone and
everyone who arrived at the site looking to work on the
coolest thing in town. And, of course, the permanent site
staff is excellent. For fellow green students, I can recommend
nothing higher than getting out there as a way of learning
about LIGO.

As of last month's newsletter, brief "locks" of the MC were
witnessed in air. After pumping down the vacuum system we still
saw only a meager 33 percent "visibility," meaning the ratio
between the locked and unlocked states of the reflected laser
power. This is a loose indication of how much power you're
getting into your cavity versus how much your shooting at it.
More recently we have seen more healthy amounts, such as 80-90
percent.

To throw out a couple numbers, the MC is designed to have a
finesse of approximately 1500, which means that it will hold
roughly 10 kW of laser power when its running at full throttle.
That's concentrated into a spot of about 1/7 of an inch on the
mirrors.

One of the more spectacular windows we have of this cavity isn't
a view at all but a sound, provided by a pair of headphones
hooked up to the output of the mixer (Figure 7, at left) on the "Demod Board" supplied
by the Control and Data System group. This is like listening to the
"heartbeat" of the thing, which seemed to have all kinds of noises
as of a few weeks ago. After strapping on the headphones, we heard
a thumping noise which led us directly to a servo oscillation.
We promptly quashed this noise source using the "Holistic Damping"
method for tuning the Small Optics Suspensions developed by MIT
graduate student Ryan Lawrence this summer. Within about a minute
and a half of putting the headphones on, this beautiful 15 meter
cavity was aligned, locked and cleaning modes. That's what I call
character.

- Contributed by Rainer Weiss

Summary of the LIGO Scientific Collaboration Meeting held at
Stanford University July 19-21, 1999.

The National Astronomical Observatory of Japan
TAMA Group joined the LIGO Scientific Collaboration (LSC). Initially, the group will work on the
development of signal recycling for LIGO II.

A near-term development plan for LIGO II was presented and discussed,
which promises to improve by over a factor of 10 the strain sensitivity
at the noise minimum, as well as to extend the observational bandwidth at
both high and low frequencies. The plan is part of the basis for a proposal
by the LIGO Laboratory to the
National Science Foundation for an upgrade to LIGO to be installed
after the LIGO I initial data run.

A draft of the LSC White Paper on Data Analysis was discussed in the data
analysis groups. Significant changes were suggested in the draft, which
will be reflected in the final draft to be issued in September 1999.

A revised LSC Publications and Presentation Policy was presented
and discussed. Small changes to the wording of the policy were suggested
and the spirit of the policy was approved. A new draft of the policy was
sent to the LSC Council for vote shortly after the meeting.